Phenol resin, use of a phenol resin as well as moulded product formed therefrom

ABSTRACT

The present invention relates to a phenol resin obtained by reacting phenolic compounds with formaldehyde and/or formaldehyde-forming compounds. The present invention furthermore relates to the use of such a phenol resin, as well as to a molded product having a core of solid, inert parts impregnated with such a phenol resin.

The present invention relates to a phenol resin obtained by reactingphenolic compounds with formaldehyde and/or formaldehyde-formingcompounds. The present invention furthermore relates to the use of sucha phenol resin, as well as to a moulded product having a core of solid,inert parts impregnated with such a phenol resin.

U.S. Pat. No. 4,116,921 relates to a resin to be used in the productionof moulded products. According to said document, such resins arecharacterized by a relatively narrow molecular weight distribution andlow molecular weight, wherein the polydispersity of such resins is low.The polydispersity ranges from about 1.5 to about 5, in particular fromabout 1.7 to about 3. Said document furthermore indicates that theduration of the reaction is determined by the desired polydispersity.Although said document comprises nine examples of exclusively bisphenolA-based resins, no further details are provided in said examples withregard to the polydispersity that is used.

International application WO 01/46101 relates to so-called stablebisphenol compositions, which are used in usual lamination processes; nospecial details are mentioned with regard to the polydispersity. Onlythe ratio between phenol and formaldehyde and the free phenol contentare mentioned as important parameters.

U.S. Pat. No. 4,337,334 relates to the preparation of a phenol resin,wherein the phenol component comprises the group of high molecularweight phenolic compounds, which latter compounds are obtained asby-products in the preparation of bisphenol A. Specific details withregard to the phenol resin are not known therefrom.

The phenol resin that is mentioned in the introduction is known per sefrom International application WO 91/19749, which has the same inventoras the present application. According to said International application,the molecular structure of the phenol resin obtained as a result of thereaction must meet a number of requirements, using a special ratio ofthe total number of reactive sites (A) in the phenol resin to the totalnumber of sites (B) in the phenol resin to which formaldehyde is added,to the total number of sites (C) in the phenol resin in which twomolecules of the phenolic compounds are condensed with each otherthrough a methylene group, which ratio is as follows:(A):(B):(C)=1:(0.85 to 1.0):(less than or equal to 0.05, in particularless than or equal to 0.02).

From International application WO 01/74750 there is furthermore known amixture which is used in the preparation of phenol resins, epoxideresins or formaldehyde resins, which starting mixture contains 35 to 75wt. % of p,p-bisphenol A, 5 to 25 wt. % of o,p-bisphenol A and 20 to 50wt. % of secondary products which are produced during the preparation ofbisphenol A, wherein the sum of the proportions by weight ofp,p-bisphenol A and o,p-bisphenol A is 50 to 80 wt. % and wherein thesum of the proportions by weight of p,p-bisphenol A and o,p-bisphenol Aand the secondary products is 100 wt. %. In particular, the mixtureadditionally contains 0 to 90 wt. % of phenol, with respect to the totalweight of the mixture then produced. Further details with regard to thephenol resin prepared with said starting material are not provided insaid document, not to mention the specific requirements that are made ofa phenol resin used in the production of rigid moulded products.

The object of the present invention is to provide a phenol resin havinga chemical-physical composition such that it is possible to use heavierimpregnation papers than in the prior art for forming moulded productsobtained by impregnating solid inert parts, in particular impregnationpaper, with phenol resin, within which impregnation papers the phenolresin distributes itself evenly.

Another object of the present invention is to provide a phenol resinhaving a chemical-physical composition such that it is possible toobtain moulded products which have a higher mechanical strength than themoulded products that are known from the prior art.

Yet another object of the present invention is to provide a phenol resinhaving a chemical-physical composition such that it is possible toobtain moulded products having a lower water absorption than the mouldedproducts that are known from the prior art.

Yet another object of the present invention is to provide a phenol resinhaving a chemical-physical composition such that it is possible to formmoulded products in which blistering will occur less easily than inprior art moulded products when such products are used in extremeconditions, viz. a higher relative humidity and high temperatures.

According to the present invention, the phenol resin as referred to inthe introduction is characterized in that the phenol resin has apolydispersity of maximally 1.85, especially preferably maximally 1.7,and a weight average molecular weight (M_(w)) of maximally 600, inparticular maximally 520.

Using such a phenol resin, it is possible to achieve one or more of theaforesaid objects. The term “polydispersity” as used in the presentdescription is a dimensionless parameter, which is known to thoseskilled in the art and which is defined as the quotient of the averagemolecular weight, M_(w), and the molecular mass that comprises thelargest number of molecules, M_(n), viz. M_(w)/M_(n). The ratioM_(w)/M_(n) can be considered to be the width of the molecular weightdistribution obtained through a GPC method. If a phenol resin having apolydispersity outside the aforesaid range is used, an unsatisfactoryimpregnation behaviour will be observed, in particular in the case ofheavier papers, which has an adverse effect, e.g. on the distribution ofthe resin in a moulded product formed of impregnation paper, and whichis thus disadvantageous with regard to the mechanical properties and thehygric values thereof.

In a special embodiment, it is especially preferable to use a weightpercentage of phenol in the phenolic compounds of maximally 95%, inparticular 25-75%. If a weight percentage of phenol of more than 95% isused, the moulded product obtained by means of such a phenol resin willexhibit shortcomings as regards its characteristics. The phenoliccompounds that are mentioned in the present invention mainly includebisphenols an polyphenols, in particular low-molecular novolacs orbisphenols and polyphenols as obtained in the preparation ofp,p-bisphenol A, for example high-molecular condensates, o,p-bisphenolA, o,o-bisphenol A, chromanes, indanes, trisphenols, ispropenylphenolsand the like, as well as the mixtures thereof.

The chemical reactions that occur in the preparation of the presentphenol resin can in fact be considered to comprise three subreactions:

1) activation

2) addition reaction, and

3) condensation reaction.

The conversion value for the addition reaction generally ranges between50 and 100%, preferably it is >90%. The conversion value of thecondensation reaction generally ranges between 0 and 50%, preferablybetween 15 and 25%. If a phenol resin that meets one or more of theaforesaid requirements is to be prepared, the conversion of volatileresin forming components, such as formaldehyde and phenol, is preferablyat least 75%, more preferably at least 90%.

When specific characteristics of a moulded product to be formed arerequired, the phenol resin may furthermore comprise one or morecomponents selected from the group consisting of fire retardants,plasticisers, fillers, colorants and binders, such as aminoplasts andthe like. Such components are used in quantities that are known to thoseskilled in the art.

The present invention furthermore relates to the use of theabove-described phenol resin for forming moulded products obtained byimpregnating solid inert parts, in particular impregnation paper, withthe phenol resin and subsequently subjecting the obtained assembly to apressing operation so as to form moulded products, using an elevatedtemperature and an elevated pressure.

Using the present phenol resin, an impregnation paper having a weight ofat least 160 g/m², in particular at least 215 g/m², may be used as theinert part. It is generally known that the commercially availableimpregnation papers have an average moisture percentage of 2.5-5%,wherein the paper weights used in the present description relate to suchcommercially available impregnation paper, which still contains a smallamount of moisture.

In a special embodiment, an impregnation paper having a weight rangingfrom 250 to 400 g/m² may be used as the inert part, which weightexhibits a satisfactory impregnation behaviour of the phenol resinprepared in accordance with the present invention.

In a specific embodiment, it is desirable to provide at least onesurface of the assembly with a decorative layer prior to or after thepressing operation.

In a specific embodiment a stationary press is used for pressing theimpregnation paper impregnated with the present phenol resin intomoulded products. On the other hand, it is also possible to use acontinuous press for such an operation.

The moulded product obtained by using the present phenol resinpreferably has a thickness varying from 0.2 to 50 50 mm, in particularfrom 0.5 to 20 mm.

The present invention further relates to the use of the present all theproduct both indoors and outdoors, wherein said outdoor use inparticular relates to the cladding or facade of buildings. Said indooruse in particular relates to the use of furniture, worktops and tabletops, storage compartments such as lockers in swimming pools and thelike.

In order to provide a better understanding of the invention, the presentinvention will now be explained by means of a number of examples, inwhich connection it should be noted, however, that the present inventionis by no means limited to such special examples. The impregnationquality ratings used in the tables below are based on a scale of 1-5, inwhich 1 means unacceptable, 2 means passable, 3 means mediocre, 4 meansgood and 5 means excellent.

COMPARATIVE EXAMPLE 1

A phenol resin was prepared by reacting pure phenol with formaldehyde,wherein phenol resins having different polydispersity values wereobtained by varying the reaction times, in particular by adding varyingamounts of catalyst. The phenol resins thus obtained were subsequentlyused for forming moulded products, with various impregnation papershaving different paper weights being used. The obtained results areshown in Table 1. The reduction of the polydispersity has anadvantageous influence on the impregnation quality, to be true, but theobtained results were still unsatisfactory for the heavier types ofpapers.

TABLE 1 Cat. Sum of volatile Impregnation quality rating Type of mol.Poly- resin forming Paper weight g/m² resin % dispersity M_(W)components % 300 254 215 160 Phenol 1 2.26 589 15.1 1 1 1 3 2 2.15 51310.6 1 1 2 3 3 2.03 474 7.4 1 1 3 4 4 1.96 468 6.0 1 2 3 4 5 1.91 4715.3 1 2 3 4 7 1.92 477 5.5 1 2 3 4

EXAMPLE 1

The operations as described above in Comparative Example 1 wererepeated, except that a 50:50 wt. % mixture of bisphenol A and phenolwas used as the starting material for preparing phenol resin. Theobtained results are shown in Table 2.

TABLE 2 Cat. Sum of volatile Impregnation quality rating Type of mol.Poly- resin forming Paper weight g/m² resin % dispersity M_(W)components % 300 254 215 160 Bisphenol 1 2.01 603 11.8 1 3 3 3 A/phenol2 1.79 481 8.1 3 4 4 4 50/50% 3 1.68 458 6.0 4 4 5 5 4 1.62 441 5.2 4 55 5 5 1.6 424 4.1 4 4 5 5 7 1.67 438 4.3 4 4 5 5

EXAMPLE 2

The operations as described above in Comparative Example 1 wererepeated, except that a 30:70 wt. % mixture of low polymeric phenols,such as bisphenols and trisphenols, by-products obtained in thepreparation of p,p-bisphenol A, on the one hand and phenol on the otherhand was used as the starting material for the preparation of phenolresin. The obtained results are shown in Table 3.

TABLE 3 Cat. Sum of volatile Impregnation quality rating Type of mol.Poly- resin forming Paper weight g/m² resin % dispersity M_(W)components % 300 254 215 160 Low 1 2.07 623 12.8 1 2 3 3 polymeric 21.77 503 9.8 2 2 4 4 phenols/ 3 1.72 475 7.4 4 4 4 5 phenol 4 1.67 4756.2 4 5 5 5 30/70% 5 1.68 472 5.2 4 4 5 5 7 1.74 487 4.8 4 4 4 4

EXAMPLE 3

The operations as described in Comparative Example 1 were repeated,except that a 60:40 wt. % mixture of low polymeric phenols, such asbisphenols and trisphenols, by-products obtained in the preparation ofp,p-bisphenol A, on the one hand and phenol on the other hand was usedas the starting material. The obtained results are shown in Table 4.

TABLE 4 Cat. Sum of volatile Impregnation quality rating Type of mol.Poly- resin forming Paper weight g/m² resin % dispersiteit M_(W)components % 300 254 215 160 Low 1 1.83 536 9.8 2 2 3 4 polymeric 2 1.66442 7.1 4 4 5 5 phenols/ 3 1.55 412 5.2 5 5 5 5 phenol 4 1.55 422 3.8 55 5 5 60/40% 5 1.58 428 3.2 4 5 5 5 7 1.65 432 3.3 4 4 4 5

EXAMPLE 4

The operations as described in Comparative Example 1 were repeated,except that a 90:10 wt. % mixture of low polymeric phenols, such asbisphenols and trisphenols, by-products obtained in the preparation ofp,p-bisphenol A, on the one hand and phenol on the other hand was usedas the starting material. The obtained results are shown in Table 5.

TABLE 5 Cat. Sum of volatile Impregnation quality rating Type of mol.Poly- resin forming Paper weight g/m² resin % dispersity M_(W)components % 300 254 215 160 Low 1 1.86 556 6.9 2 3 3 3 polymeric 2 1.62486 3.2 4 4 4 5 phenols/ 3 1.54 439 2.1 4 4 5 5 phenol 4 1.55 434 1.8 55 5 5 90/10% 5 1.58 442 2 4 4 5 5 7 1.68 454 2.1 4 4 4 5

EXAMPLE 5

The operations as described in Comparative Example 1 were repeated,except that a 80:20 wt. % mixture of polyphenols (higher-polymericphenols) and phenol was used as the starting material. The obtainedresults are shown in Table 6.

TABLE 6 Cat. Sum of volatile Impregnation quality rating mol. Poly-resin forming Paper weight (g/m²) Type resin % dispersity M_(W)components 300 254 215 160 Polyphenol/ 2 2.01 685 3.9 1 1 1 1 phenol 31.94 591 3.0 1 1 2 2 80/20 4 1.81 612 2.7 1 1 2 2 5 1.83 580 2.6 2 2 3 4

TABLE 7 Resin Impregnation distribution of Mechanical Hygric valuesquality rating the paper strengths (swelling) Blistering 1 − − − − 2 − 0− − 3 0 0 0 0 4 + 0 + + 5 + + + + − means poorer than average 0 meansaverage + means above average

The impregnation quality rating that is included in Tables 1-6 is basedon a scale of 1-5, in which 1 means unacceptable, 2 means passable, 3means mediocre, 4 means good and 5 means excellent. In Table 7 theseratings 1-5 for the impregnation quality are related to the resindistribution, the mechanical properties, the hygric values and thetendency to form blisters. Furthermore it should be noted that theaforesaid phenol resins were all prepared under reflux conditions at atemperature of less than 105° C., wherein, after condensation, theviscosity of the resins thus prepared was set at a value of 200 cP withthe addition of a solvent. The average molecular weight M_(w) and themolecular mass comprising the largest number of molecules, M_(n), weredetermined by means of gel permeation chromatography. The polydispersitylisted in Tables 1-6 is M_(w)/M_(n). The impregnation quality listed intables 1-6 was assessed by subjecting the resin-impregnated impregnationpapers to a pressing operation in a standard pressing cycle, after whicha so-called bevel was milled off the plate thus obtained, and thehomogeneity of the milled surface was assessed.

From the aforesaid Tables 1-6 it follows that the use of a paper weightof e.g. 300 g/m² for a resin obtained from pure phenol (see ComparativeExample 1) having a polydispersity ranging from 1.91 to 2.26 leads to anunacceptable impregnation quality, in spite of the fact that the weightaverage molecular weight is less than 600. On the other hand, if a 50:50wt. % mixture of bisphenol A and phenol is used as the starting materialfor preparing phenol resin (see Example 1), a good impregnation qualityis obtained at a polydispersity of 1.68 and an M_(w) of less than 500,using a paper weight of 300 g/m². According to Example 2, a goodimpregnation quality is obtained for a paper weight of 300 g/m² if apolydispersity value of 1.72 is used, using a 30:70 wt. % mixture oflow-polymeric phenols and phenol as the starting material. From Table 4it follows that the further reduction to 40% of the weight percentage ofphenol in the starting material mixture having a composition oflow-polymeric phenols and phenol leads to a lower polydispersity value,wherein a polydispersity of 1.55 and an M_(w) of less than 450 leads toan excellent impregnation quality for a paper weight varying from 160 to300 g/m². When the amount of phenol in a starting material consisting ofa 90:10 wt. % mixture of low-polymeric phenols and phenol is reducedeven further (see Example 4), it appears that a polydispersity value of1.86 leads to a mediocre impregnation quality for a paper weight of 254g/m² and a passable impregnation quality for a paper weight of 215 g/m².Table 6 clearly shows that a polydispersity lower than 1.85 incombination with an M_(w) higher than 600 leads to an unsatisfactoryresult.

From the aforesaid experimental results it follows that a polydispersityof maximally 1.85 and a weight average molecular weight of maximally 600makes it possible to form heavier impregnation papers into a desiredmoulded product whilst maintaining a good resin distribution, whereas inthe case of pure phenol resins a satisfactory impregnation behaviour isonly obtained with low-value paper weights. A moulded product having agood impregnation quality has significantly better characteristics thana poorly impregnated moulded product, in particular a higher mechanicalstrength, a lower water absorption and a decreased tendency to formblisters, when such a product is used under severe conditions, inparticular a relative humidity of 100% and high temperatures.

1. A phenol resin consisting essentially of a reaction product obtainedby a process consisting essentially of reacting phenolic compounds withformaldehyde and/or formaldehyde-forming compounds, wherein the phenolresin has a polydispersity of maximally 1.85 and a weight averagemolecular weight (M_(w)) of maximally
 600. 2. The phenol resin accordingto claim 1, wherein said phenol resin has a polydispersity of maximally1.7.
 3. The phenol resin according to claim 1, wherein said weightaverage molecular weight (M_(w)) is maximally
 422. 4. The phenol resinaccording to claim 1, wherein the weight percentage of phenol in thephenolic compounds is maximally 95%.
 5. The phenol resin according toclaim 1, wherein the weight percentage of phenol in the phenoliccompounds ranges between 25 and 75%.
 6. The phenol resin according toclaim 1, wherein the phenolic compounds comprise bisphenols andpolyphenols.
 7. The phenol resin according to claim 1, wherein said thephenolic compounds comprise low-molecular novolacs.
 8. The phenol resinaccording to claim 6, wherein said bisphenols comprise p,p-bisphenol A.9. The phenol resin according to claim 1, wherein the conversion ofphenolic compounds, formaldehyde and/or formaldehyde-forming compoundsis at least 75%.
 10. The phenol resin according to claim 1, wherein theconversion of phenolic compounds, formaldehyde and/orformaldehyde-forming compounds is at least 90%.
 11. The phenol resinaccording to claim 1, wherein the phenol resin furthermore comprises oneor more components selected from the group consisting of fireretardants, plasticisers, fillers, colorants and binders.
 12. A methodfor forming moulded products by impregnating solid inert parts with aphenol resin to form an assembly, and subsequently subjecting theobtained assembly to a pressing operation at an elevated temperature andan elevated pressure so as to form moulded products, which phenol resinconsists essentially of a reaction product obtained by a processconsisting essentially of reacting phenolic compounds with formaldehydeand/or formaldehyde-forming compounds, wherein the phenol resin has apolydispersity of maximally 1.85 and a weight average molecular weight(M_(w)) of maximally
 600. 13. The method according to claim 12,comprising an impregnation paper having a weight of at least 160 g/m² asthe solid inert part.
 14. The method according to claim 12 comprising animpregnation paper having a weight ranging between 250 and 400 g/m² asthe inert part.
 15. The method according to claim 12, wherein at leastone surface of the assembly is provided with a decorative layer prior toor after said pressing operation.
 16. The method according to claim 12,wherein a stationary press is used for pressing the moulded products inthe pressing operation.
 17. The method according to claim 12, wherein acontinuous press is used for pressing the moulded products in thepressing operation.
 18. A moulded product having a core of solid inertparts impregnated with a phenol resin, which phenol resin consistsessentially of a reaction product obtained by a process consistingessentially of reacting phenolic compounds with formaldehyde and/orformaldehyde-forming compounds, wherein the phenol resin has apolydispersity of maximally 1.85 and a weight average molecular weight(M_(w)) of maximally
 600. 19. The moulded product according to claim 18,wherein the thickness of the moulded product ranges between 0.2 and 50mm.
 20. The moulded product according to claim 18, wherein the thicknessof the moulded product ranges between 0.5 and 20 mm.